Liquid crystal display ("LCD") modules are commonly employed to display alpha-numeric data such as date and time in timepieces, numerals in calculators, data stored in memory devices and a host of other applications where data display has been incorporated into a product. For example, it has become common in recent years to incorporate alpha-numeric LCD modules into camera bodies in order to display data to the photographer relating to film type, image frames remaining on the film cartridge, exposure parameters, flash illumination parameters and other camera status data. Such liquid crystal display modules are incorporated in the Kodak.RTM. S500 camera body for displaying such data to the photographer.
The liquid crystal display element or "glass" of such LCD modules has become widely employed in standardized and customized component versions in the industry. The liquid crystal display material is layered and sealed between the mating or inner surfaces of upper and lower planar glass substrates on which nearly transparent, conductive, planar ground electrodes and segment shaped electrodes are formed, respectively. Upper and lower planar polarization layers, rotated at 90.degree. polarization to one another, are adhered to the exterior surfaces of the upper and lower substrates. A reflective or mirror layer is adhered to the lower polarization layer.
The layers of liquid crystal display organic molecules are formed to exhibit interference patterns and light polarization when not influenced by an electrical field. In the absence of applied voltage, LCD material layers between the parallel ground and segment electrodes rotate polarized light passing through the upper polarization layer and allows it to be passed through the lower polarization layer and be reflected back, providing the bright background of the display 12. Depending upon the magnitude of the voltage applied between the parallel planar electrode and the segment electrodes, dark alpha-numeric characters are formed on the light background by a reorganization of the molecules between the ground and the segment electrodes which does not display polarized light rotation. The non-rotated light is blocked from striking the reflective mirror by the lower polarization layer, resulting in the dark character segments. Because LCD devices have a very high internal impedance, the current drawn by the device is small, making LCD's desirable for low current drain applications, e.g. battery operated cameras.
The LCD glass is usually rectangular in configuration and has at least one linear array of conductor terminal aligned pads along one edge of the upper glass substrate thereof. The conductor terminal pads are connected by nearly transparent conductive paths to the segment electrodes and the planar ground electrode formed on the interior surfaces of the lower and upper substrates.
The LCD glass is typically mounted in association with a further substrate or printed circuit board having a pattern of conductive pathways or printed circuit conductors extending to and from a chip-on-board mounted integrated circuit and terminal pads formed on a surface thereof. Certain of the terminal pads are formed in a further linear array that is positioned in alignment with the linear array of terminal pads on the LCD glass by a mounting assembly. The LCD glass is typically spaced apart from the substrate or printed circuit board and supported by a non-conductive plastic spacer element in a sandwiched configuration. The spacer element also positions the terminal pads of the LCD glass in vertical alignment with the matching terminal pads of the printed circuit board. An electrical connection is made between the aligned terminal pads employing a flexible connector strip to interconnect the respective terminal pads on the parallel. surfaces of the LCD glass substrate and the printed circuit. The LCD glass, connector strip, spacer element, and printed circuit board are held together by mounting bolts, screws, clips or accessory pieces that hold the sandwiched components of the LCD module together.
The flexible connector strip extends in the "Z"-direction between the aligned linear arrays of terminal pads on the parallel LCD glass and printed circuit board, whereas each terminal pad is connected to a respective conductive pathway or printed circuit conductor extending in the "X" and "Y"-directions on the surface of the respective substrate or printed circuit board. Such connector strips are formed of alternate conducting and insulating layers of an elastomeric, compressible material. Such connector strips are obtained from a number of manufacturers, including Technical Wire Products, Inc. of Cranford, N.J., which characterizes the connector strips as "Zebra" strips, and AMP Incorporated of Harrisburg, PA.
Preferably, the conducting layers of the connector strip are formed of non-woven carbon fibers impregnated with silicone rubber and the insulating layers are formed of pure silicone rubber. Because the connector strip is made of resilient elastomeric materials, it is highly tolerant of uneven surfaces and may be compressed so that the high modulus of the fibers allows them to penetrate any surface oxides on the mating surface, while the resiliency of the elastomer allows the connector to conform to irregular or warped surfaces. The conductors also move slightly in a lateral direction to provide a contact wipe during compression.
There are numerous examples of the use of such connector strips in assemblies of printed circuit boards, LCD modules, etc., as shown in U.S. Pat. Nos. 4,422,728; 4,545,647; 4,598,960; 4,643,499; 4,652,973; 4,878,738; and 5,033,970.
Data and control signals for operating the drive circuit for the LCD glass display are applied to input terminals of the driver IC in the chip-on board, and battery voltage and system ground are connected to both the display glass and to the driver IC through a flat, thin, multi-conductor, flexible film system or "flex circuit" of the type described, for example, in U.S. Pat. No. 4,655,551. In camera applications, the flex circuit extends between and is routed from the battery and various sensors and electro-mechanical camera mechanisms through narrow spaces inside the camera housing. The flex circuit is custom shaped and sized to fit a particular camera and eliminates a bulky wiring harness.
Generally, in camera manufacturing, it is desirable to reduce the number and size of separate components and the cost of assembling the camera from the components. The attachment of the flexible circuit to the printed circuit board of the LCD module of the above mentioned camera involves soldering its terminals to terminal pads on an exterior surface of the printed circuit board of the assembled LCD module.
Linear terminal pad arrays formed at the edge of printed circuit boards as male terminals may also connected to flexible circuits by mating female connectors.
In the '551 patent, a large scale LCD display is fabricated from the assembly of one or more drive flex circuits each carrying an IC chip, e.g. and LSI chip, in a film carrier type assembly into the layers of the flex circuit. Each such drive flex circuit has a set of input and output terminal pads or electrodes, wherein the output terminal pads are aligned with a connector strip for electrical connection to a linear array of LCD glass terminal pads, and the input terminal pads are aligned with terminal pads or electrodes of a further, transversely oriented, flex circuit. The transversely oriented flex circuit operates as a bus structure for distributing power and data signals to the one or more drive flex circuit. The assembly of the drive and bus flex circuits with the connector strip and LCD glass is accomplished by clamping these components against a base plate or to one another, without a base plate. The respective mating terminal pads of the bus and drive flex circuits are bonded or soldered together.
Other methods for electrically connecting LCD glass to flexible or hard printed circuits include cementing individual connector pins directly on the LCD glass in contact with the terminal pads with conductive adhesive, inserting the pins into holes in the printed circuit terminal pads, and soldering the pins to the surrounding terminal pads, which is labor intensive and does not take advantage of the flexible connector strips. This same approach may be employed in simply attaching flexible circuits to printed circuit terminal pads by pins extending from the printed circuit board terminal pads and through mating holes in the terminal pads of the flexible circuit and soldering the connections, which again is labor intensive and not easy to disassemble.